Incendiary composition including zinc-mischmetal alloy

ABSTRACT

INCENDIARY COMPOSITIONS CHARACTERIZED BY LONG-BURNING QUALITIES AND RETENTIVE INCANDESCENT ASH COMPRISE FINELY DIVIDED HEAVY METAL AS FUEL AND OXYGEN-CONTAINING POLYMER AS BINDER AND OXIDIZER, E.G. MIXED RARE EARTH METAL OF THE LANTHANIDE SERIES AND ACRYLIC-TYPE POLYMER. THE COMPOSITIONS FIND PARTICULAR UTILITY IN MAKING INCENDIRY BOMBS THAT HAVE IDENTICAL BALLISTICS WITH EXPLOSIVE FRAGMENTARY BOMBS.

United States Patent 01 hce 3,809,586 Patented May 7, 1974 U.S. Cl. 149--19.91 9 Claims ABSTRACT OF THE DISCLOSURE Incendiary compositions characterized by long-burning qualities and retentive incandescent ash comprise finely divided heavy metal as fuel and oxygen-containing polymer as binder and oxidizer, e.g., mixed rare earth metal of the lanthanide series and acrylic-type polymer. The compositions find particular utility in making incendiary bombs that have identical ballistics with explosive fragmentary bombs.

CROSS-REFERENCE TO RELATED APPLICATION Reference is made under the provisions of 35 USC 120 to earlier filed copending application Ser. No. 840,211, filed July 9, 1969, for Incendiary Compositions and Devices (now abandoned).

BACKGROUND OF THE INVENTION While the science of pyrotechnics is old, it has been, in recent years, the subject of countless innovations, as increasing applications are discovered, consequent on discoveries of new materials and new combinations of materials. Some slow-burning, low heat output compositions have been devised for heating combustibles at camp sites or the like. In contrast, there are high heat output and short-burning compositions which are used for welding, military incendiary applications and the like, e.g., thermite-type products Which are mixtures of powdered aluminum and ion oxide. Other metal-fuel pyrotechnics have been developed employing powdered magnesium in conjunction with oxidizers including fluorocarbon materials, e.g., see U.S. 3,122,462 and 3,152,935.

In the field of incendiary devices, the majority of known compositions utilize either hydrocarbon fuels contained in a jellied matrix or light-weight metal-fuel incendiary products, including thermite-type materials, e.g., powdered light metals, such as aluminum or magnesium, in combination with oxidizers. Both of these groups of compositions have certain inherent disadvantages. For example, the relatively light weight of these materials and their low bulk density seriously limit the terminal velocity and penetration ability of devices incorporating them when air-dropped onto a target. Also, area coverage of such incendiary products, when explosively disseminated, is relatively poor because of their low density. Such relatively low density incendiary products also present diificulties from the military viewpoint since incendiary bombs which contain these products cannot be made to have identical ballistics with explosive bombs, and this prevents or inhibits the air-dropping of mixed loads of incendiary and explosive bombs accurately into the same target area.

Although the great bulk of the incendiary compositions utilized for military or industrial applications, involve light weight metals or other light fuels, it is also known to employ heavy metals such as titanium, zirconium and the like as fuel materials in pyrotechnic compositions. For example, U.S. Pat. 3,006,745, concerns the use of metal soap in combination with a powdered metal fuel to enhance, and produce ultra high heating temperatures upon combustion of the fuel. Pyrotechnic compositions with longburning qualities and retentive incandescent ash formed of heavy metals or metal hydrides and solid fluorocarbon polymer as oxidizer are disclosed in U.S. Pat. 3,565,706.

It is also known to make pyrotechnic compositions by combining a subdivided metallic fuel with a polymer binder (see U.S. Pat. 3,180,770); to use a nitro-containing polymer containing a fuel in combination with an added oxidizer (see U.S. Pat. 3,266,959; and to use a polymer made from an acrylate-type monomer, catalyzed with strontium perchlorate as fuel and oxidizing agent for pyrotechnic compositions (see U.S. Pat. 3,369,946).

Notwithstanding the vast amount of research and development work which has occurred in the field of pyrotechnic compositions, further improvements are needed, particularly in the art of providing long-burning compositions having maximum incendiary effectiveness in making incendiary bombs and other similar military applications.

A principal object of this invention is to provide new and improved incendiary compositions and devices.

Other objects and scope of applicability of the invention will become apparent from the detailed description given herein; it should be understood, however, that the detailed description, while indicating preferred embodiments of the invention, is given by way of illustration only; and that various changes and modifications, within the spirit and scope of the invention, will become apparent to those skilled in the art from this detailed description.

SUMMARY OF THE INVENTION These objects are accomplished according to the present invention in part by preparing incendiary compositions having a specific gravity ranging from 2.0 to 4.5, comprising a finely-divided heavy metal fuel and a solid, oxygencontaining polymeric material, which serves as an oxidizerbinder.

The objects are also in part accomplished by forming incendiary compositions to contain as fuel a mixture of two or more metals that react at an elevated temperature to form an alloy or compound with an appreciable exotherm.

In a preferred embodiment of the invention, the new incendiary compositions consist essentially of powdered metal material distributed uniformly throughout a matrix of solid oxidizer material wherein:

(a) said metal material is at least 50% by weight heavy metal selected from the group consisting of metals of Group II-A, II-B, III-B or V-B of the Periodic Table, the hydrides of such metals and mixtures thereof, said metal material being of particle size between about 1 and 300 microns,

(b) said solid organic polymer containing only carbon, hydrogen and oxygen consisting essentially of a copolymer of glycidyl methacrylate and an acrylic estertype monomer containing at least two groups of the formula wherein R is hydrogen or CH and (d) the mol ratio of said metal material to said solid oxidizer material is between about 1-15 to 1.

The preferred technique for producing the new products of the invention involves first preparing a polymerizable mixture of monomer, or cornonomers, and a polymerization catalyst, incorporation in the polymerizable mixture finely-powdered metal, and thereafter casting or otherwise shaping the resulting monomer and metallic fuel material mixture and subjecting the shaped mass to polymerization or curing conditions to convert the mass into a solid-elastic or hard structure. Incendiary compositions formed in this manner may utilize only heavy metals of the type hereinafter defined. Optionally, nickel, copper and/or light-weight fuel materials or metals may be included in these compositions, such as magnesium, aluminum, or boron. In this manner, lower density composition may be prepared using varying ratios of finelydivided magnesium, aluminum, and/or other light-weight material, in combination with the finely-divided heavy metal fuel.

Advantageously, one uses alloys of lanthanide elements as the principal fuel component of the new compositions. These alloys are available as by-products of rare element metal refining operations, commonly called mischmetal. However, other heavy metal fuels may be used. The term heavy metal as used herein and the appended claims means a metal of atomic number greater than 20 selected from Groups II-A, II-B, III-B, IV-B or V-B of the Periodic System of the Elements. Additionally, the hydrides of such metals may be used as well as mixtures of such metals, mixtures of such hydrides or mixtures of the metal and hydrides.

The stated groups of metals are to be understood to be:

Group II-Astrontium, barium and radium.

Group II-B-zinc, cadmium and mercury.

Group I]IB-scandium, yttrium, lanthanum series metals (Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) and actinium series metals (Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, E, Fm, Mn and No).

Group IV-Btitanium, zirconium and hafnium.

Group V-B-vanadium, niobium and tantalum.

Because of safety and treaty considerations, it is preferred not to use radioactive metals although these are operative.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following details of operations and reported data illustrate the further principles and practice of the invention to those skilled in the art. In these examples, and throughout the remaining specification and claims, all parts and percentages are by weight unless otherwise specified.

Example 1 Three separate incendiary compositions A, B and C were made from the ingredients listed below and in the parts stated:

Ingredient A B C Glyeidyl methacrylate 72 6 'Inmethylol propane trimethacryla Z-ethylhexyl acryla Butylene dimethacrylate Potassium nmt'e'IIIIIIIIIII Alloy oi 67.5% lanthanide elements and 32.5%

zinc (alloy 675L) 336. 9 71. 27

The ingredients of each composition were thoroughly Example 2 4 parts of glycidyl methacrylate 2 parts of Z-ethylhexyl acrylate 0.5 part of 1,3-butylene dimethacrylate 13.5 parts of 2-nitro-3-methyl-propyl-methacrylate parts of Alloy 675L 75 The mixture was polymerized to a hard, dense casting by having the monomers catalyzed with benzoyl peroxide and dimethyl toluidine activator. Combustion of this cured mass of material was smooth and without scintillation (burning particles of metal ejected from the surface). The mass remained intact to leave an incandescant ash that continued to burn in air for 30 minutes.

Example 3 4 parts of 2-ethylhexyl acrylate 30 parts of 2-nitro-3-methyl-propyl methacrylate 1 part of trimethylolpropane trimethacrylate 65 parts of Alloy 675L The mixture was catalyzed with 1 part of benzoyl peroxide and promoted with 0.1 part of N,N-dimethyl-toluidine, then polymerized slowly to a tough solid. The composition burned vigorously for 5 minutes and the remaining mass continued to burn in air for minutes with intensive heat radiation following ignition with butane flame.

Example 4 34 parts of 2-nitro-2-methyl-propyl methacrylate 1 part of trimethylolpropane trimethacrylate 65 parts of zirconium This composition was catalyzed and promoted, as in Example 3, setting to an elastic solid in several hours. When ignited, the sample burned slowly until the binder was nearly exhausted. After 5 minutes, an exothermic reaction heated the entire mass to incandenscence within 15 seconds. The mass continued to burn in air for 2 hours.

Example 5 36.47 parts of glycidyl methacrylate 26.47 parts of 2-nitro-2-methyl-propyl-methacrylate 1.80 parts of trimethylolpropane trimethacrylate 334.65 parts of an alloy of 70% lanthanide elements and 30% copper This composition was polymerized in the manner of Example 1 to a hard solid. Combustion of the mass was slower than observed for the product of Example 1, but the incandescent residue was exceptionally hard and retained the features of the original incendiary configuration.

Example 6 A polymerizable composition was formed of the following ingredients:

8.86 parts of glycidyl methacrylate 8.86 parts of 2-nitro-2-methyl-propyl methacrylate 0.44 part of trimethylolpropane trimethacrylate 81.30 parts of an alloy of 67.5% lanthanide elements and 32.5% zinc A portion of the mixture was cast into a mold in which there was centrally suspended an impact detonator, fuse and igniter device to form a bomblet. Various forms of fuses and ignition trains may be used in making bomblets or other military or industrial devices from any of the new incendiary compositions of the invention.

Another portion of the composition was cast into test coupons that were subjected to standard Parr calorimeter determinations. This revealed a heat of reaction for the cured incendiary mass in argon of 263 calories/gram. The heat of combustion in oxygen was 1910 calories/gram. The heat of combustion in oxygen of the metal alloy alone was 1523 calories/gram.

Example 7 22.2 parts of 2-nitro-2-methyl-propyl methacrylate 0.6 part of trimethylolpropane trimethacrylate 53.6 parts of atomized aluminum 23.6 parts of powdered nickel Example 8 Polymerizable compositions I and II were formed by mixing together the following ingredients in the parts indicated:

Ingredient I Glycidyl methacrylate 'Irimethylolpropane trimethacrylat Benzoyl peroxid Potassium nitrate. Sodium oxalate.

The alloy consisted of 67.5% mischmetal and 32.5%

Following the mixing of the ingredients of each composition, they were cast into a mold and allowed to stand at ambient temperature (-25 C.) to polymerize into a solid mass. The resulting molded solid incendiary products combusted smoothly on ignition and remained intact to leave an incendiary ash that continued to burn in air for at least 30 minutes. In other cases, alloys containing 50-96% mischmetal and 4-50% zinc were used in forming compositions with satisfactory burning properties. Such alloys exhibit insensitivity to corrosion by moisture and satisfactory ability to be ball milled for particle size reduction.

DISCUSSION OF DETAILS The success of the invention is, in part, due to the discovery that mixtures comprising finely-divided heavy metal fuel and oxygen-containing polymer binder provide pyrotechnic products that undergo an initial combustion at a relatively rapid rate, forming non-fluid retentive incandescent ash, which is of such nature or form that it can continue to combust with the oxygen present in the surrounding atmosphere. The result is that the incendiary material remains incandescent for an extended period, e.g., 15 minutes to 2 hours, and is capable, during that time, of supplying heat for useful purposes and/or of serving to ignite part of a military target against which it is directed. Incendiary compositions formed in accordance with the invention provide greater total heat output per unit volume and much longer burning time than metal-fuel incendiary compositions that have been previously known.

Another contribution of the invention is the discovery that certain oxygen-containing polymers can be used both as binders and sole oxidizers in compositions prepared in accordance with the teachings of the invention. While some of these polymers have been used before in pyrotechnic compositions, either as binders, or as oxidizers aided with other oxidizing additions, the discovery herein lies in their utility as oxidizers without the aid of additional oxidizing materials.

The inclusion of additional oxidizers in amounts ranging from 0 to 50%, particularly 12-O%, by weight of the total oxidizer content, provide another embodiment of the invention. Such other oxidizers are well known in the art and include ammonium and metal salts, e.g., ni-' trates, perchlorates, perborates, oxalates, as Well as oxides and peroxides, as well as other oxidizing ma terials.

A variety of materials are available for use as oxygencontaining polymers that serve as oxidizers-binders in accordance with the invention. In general terms, these include:

acrylic type polymers vinyl ester polymers allyl ester polymers 'vinyl ether polymers vinyl ketone polymers epoxy resins Both monofunctional and polyfunctional oxygen containing polymerizable monomers may be used in forming the polymers which may be homopolymers or copolymers. The copolymers in a preferred embodiment are prepared from monomers that contain only carbon, hydrogen and oxygen atoms.

Acrylic type of polymers are particularly useful for the invention. Such polymers are formed by homopolymerization or copolymerization of material containing at least 50% of monomer having the general formula:

wherein R is halogen, H or CH n is an integer 1, 2 or 3 R is hydrogen or an organic radical derived from a compound having at least n esterifiable hydroxyl groups. Preferably R contains between 1 and 24 carbon atoms and especially 1 to 12 carbon atoms, is acyclic and contains only carbon, hydrogen and oxygen atoms.

Specific examples of monomers from which the acrylic type polymers may be formed include:

glycidyl methacrylate trimethylolpropane trimethacrylate 2-ethylhexyl acrylate 2-nitro-2-methylpropyl methacrylate 1,3-butylene dichloroacrylate methyl 2-chloroacrylate ethyl fluoroacrylate glycol diacrylate 1,3-butylene dimethacrylate 2-nitrobutyl acrylate 2,2-dinitrohexyl methacrylate trifluoromethyl methacrylate propyl ot-bromoacrylate methyl methacrylate ethyl methacrylate butyl methacrylate methyl acrylate hexyl acrylate octyl acrylate vinyl methacrylate fi-amino ethyl acrylate N,N-dimethyl aminoethyl acrylate acetate allyl methacrylate methacrylic acid acrylic acid 2-chloroacrylic acid acrylamide methallyl acrylate pentafluorophenoxy acrylate A preferred group of incendiary materials of the invention are made by copolymerization of to 99% glycidyl methacrylate with 1 to 10% of a polyunsaturated monomer of the formula:

wherein R is H or ---CH;,

n is the number 2 or 3 Z is a hydrocarbon radical containing 2 to 10 carbon atoms.

In another embodiment, the radical Z is a nitrohydrocarbon radical containing 3 to 12 carbon atoms and l or 2 nitro-groups.

Examples of other monomers that may be used in forming the oxygen containing polymers include:

vinyl acetate vinyl methyl ether divinyl ether vinyl hexyl ketone N-vinyl pyrrolidone itaconic acid crotonic acid diethyl fumarate acrolein vinyl stearate maleic anhydride dimethyl maleate diallyl-3,5-dimethyl phthalate diallyl phthalate.

Copolymerizable materials may be included in the oxygen-containing polymers for various purposes, such as to harden the polymer by cross-linking to render them elastomeric, to modify the burning rate, to increase adhesion to the fuel material, to increase or decrease the polymerization rate, and so forth. The copolymerizates may be monofunctional or polyfunctional. Specific examples of monofunctional comonomers include:

vinyl chloride vinylidine chloride propylene methyl styrene cyclopentadiene acrylom'trile 2-vinyl pyridine styrene 2,5-dichlorostyrene tetrafiuoroethylene 4-vinyl cyclohexene Specific examples of polyfunctional comonomers include:

divinyl pyridine divinyl benzene divinyl toluene Another noteworthy feature of the invention is the ability of obtaining a variety of Pilling-Bedworth ratios with a basic combination of metal-fuel and oxidizer by varying mixtures of the metals and ratio of fuel to polymer. The permits the area covered by the incandescent ash of the basic combination to be controlled as required by special applications. An active fuel metal component of lesser density than the principal metal fuel component may be used, e.g., magnesium, aluminum, boron, the hydrides of these metals, organometallic compounds, or the like.

The exact amount of such additives will be varied depending, in part, upon the specific additives used and, in part, upon the Pilling-Bedworth ratio that is desired.

Incendiary compositions particularly useful for making incendiary bombs and related military incendiary devices contain the following ingredients in the parts stated:

Parts Oxygen-containing polymer 5-80 Powdered metal fuel 100 In more detail, preferred cured compositions of the invention will consist of:

Parts Acrylate type polymer 10-80 Lanthanide series metal Zinc 10100 An acrylate type polymer found particularly useful for military bomb production is formed of the following com bination of monomers:

Parts Glycidyl methacrylate 100 Trimethylolpropane trimethacrylate 2-8 Preferred metals are zinc, zirconium, tantalum, vanadium and lanthanum series alloys. Mischmetal, which is primarily a mixture of rare earth metals of the lanthanum series, is an example of a metal fuel which may be advantageousl used. A typical mischmetal would comprise Ce, La, Nd, Pr, and Ba. Other elements advantageously used as fuel material in the new compositions are Y, La, l-lf, Nb, and Ti.

The metal fuel material should be finely subdivided for combination with the oxidizer-binder, advantageously to between about 1 and 300 micron size. Such material can be prepared by any suitable comminution method, e.g., ball milling, rod milling, roller grinding, pug milling, etc., and may be used directly or pre-coated with a thin layer of ignition, primer, or other material, washed with monomer or the like. If pre-coated, 0.1 to .5% of coating is recommended.

In forming the new pyrotechnics, the finely divided metallic fuel material is preferably homogenously mixed with the monomer or monomer mixture or partially polymerized material. Degassing of the powdered fuel material, pre-coating as previously mentioned, or any similar treatments known to the polymer art for aid in compounding pigments or powders with polymerizable monomers or prepolymers may be employed in conducting these operations. Standard catalysts such as peroxides, persulfates, diazo compounds and the like are advantageously used to convert the monomer into the required solid polymer. So-called promoters, e.g., aromatic amines such as N,N-dimethyl-p-toluidine, are useful in effecting the polymerization and curing at low temperatures, e.g., 0- 50 C. High temperatures are naturally to be avoided to mitigate the possibility of premature ignition. The catalysts and the promoters are preferably used in concentrations each of 0.01 to 3% of the total monomer mixture.

The ratio of oxygen-containing polymer to metal fuel may be varied between about 1:1 and 1:500 to give a heat of reaction in argon of at least calories per gram. The maximum for such value may be as high as desired, e.g., up to 350 cal./ gm. The binder to metal fuel proportions are mainly controlled to give the necessary ballistics.

The oxygen-containing polymer not only acts as an oxidizer during the initial combustion of the metal fuel, but its presence also causes the ash to remain as a coherent mass. The compressed metal in the absence of the polymer gives a non-coherent ash.

The new pyrotechnic compositions may be ignited by heat alone or by chemical igniter agents. When ignited, they burn reliably leaving a coherent incandescent residue or ash. Thus, compositions that have a fuel material content that is at least 50% or greater heavy metal, burn to form incandescent residues which maintain heat suflicient to ignite wood, cloth, leaves, etc., for 90 minutes or longer, if the combustion residue is left undisturbed. In some instances, e.g., compositions containing zirconium as the major fuel material, the residue or ash reaches incandescence slowly, apparently as a result of a secondary reaction with air. This phenomenon may occur in vigorous fashion as long as 10 minutes after the initial combustion of the oxidizer-binder. The residue of all products of the invention are capable of igniting wood and similar combustables, subsequent to the full initial combustion of the oxidizer-binder. In addition, the residues from the exothermic alloying reactions are capable of cutting or welding metal structures.

Incendiary bombs prepared according to the teachings of the invention, may take any desired form known to the art. It is possible to air-drop mixed loads of incendiary bombs and explosive bombs with accuracy into the same target area. Furthermore, upon ignition of the incendiary charge of such bombs, retentive incandescent ash or residue will remain in the target area in active combustible igniting conditions for extended periods, e.g., up to two hours.

The embodiments of the invention in which an exclusive property or right is claimed are defined as follows:

1. An incendiary material in the form of a solid article having a finely divided metal distributed uniformly throughout a matrix of solid material formed by polymerization of a mixture comprising the following ingredients in the parts by weight as stated:

Parts Glycidyl methacrylate 1700-1800 Trimethylolpropane trimethacrylate 40-50 Solid additive 100-1000 Mischmetal zinc alloy containing about 67.5%

mischmetal and about 32.5% zinc 7000-8000 Parts Glycidyl methacrylate 1800 Trimethylolpropane trimethacrylate 43 Benzoyl peroxide Potassium nitrate 650 Mischmetal zinc alloy containing 67.5% mischmetal and 32.5 zinc 7477 4. The incendiary material of claim 1 formed from a mixture consisting of the following ingredients in about the parts by weight as stated:

Parts Glycidyl methacrylate 1700 Trimethylpropane trimethacrylate 40 Benzoyl peroxide 30 Sodium oxalate 300 Mischmetal zinc allo containing 67.5% mischmetal and 32.5% zinc 7930 5. An incendiary material in the form of a solid prodduct having finely divided metal distributed uniformly throughout a matrix of solid material formed by the polymerization of a liquid mixture in the presence of a catalyst, said incendiary material consisting essentially of: (a) metal alloy consisting of about 67.5% mischmetal and about 32.5 zinc,

(b) solid matrix material consisting essentially of solid organic polymer and up to 30% metal salt oxidizer, (c) said solid organic polymer is a copolymer of 90- 99% glycidyl methacrylate and 1-10% trimethylol propane trimethacrylate,

(d) said metal alloy constitutes at least 50% of said mixture and (e) said solid matrix material is present in an amount at least sufiicient to give the incendiary material a heat of reaction in argon of at least 190 calories per gram. 6. An incendiary material in the form of a solid article having finely divided metal distributed uniformly throughout a matrix of solid polymer formed by polymerization in the presence of a catalyst of a mixture of the following ingredients in the parts stated:

Parts Glycidyl methacrylate 886 2-nitro-2-methyl propyl methacrylate 886 Trimethylolpropane trimethacrylate 44 Alloy of 67.5 lanthanide series metals and 32.5%

zinc 8 7. An incendiary material in the form of a solid article having finely divided metal distributed uniformly throughout a matrix of solid polymer formed by polymerization of a mixture comprising the following ingredients in the parts stated:

Parts Glycidyl methacrylate 1800 Butylene dimethacrylate 40-50 Benzoyl peroxide 30-35 Inorganic nitrate 800-1000 Metal alloy 7000-7500 said inorganic nitrate being barium or potassium nitrate and said metal alloy consisting of 67.5 lanthanide elements and 32.5 zinc.

8. An incendiary material as claimed in claim 7 wherein said mixture consists essentially of:

Parts Glycidyl methacrylate 1800 Butylene dimethacrylate 43 Benzoyl peroxide 30 Barium nitrate 1000 Metal alloy 7127 9. An incendiary material as claimed in claim 7 wherein said mixture consists essentially of:

OTHER REFERENCES Grant, Hackhs Chemical Dictionary, 4th ed., p. 481, McGraw-Hill Book Company (1969), New York.

LELAND A. SEBASTIAN, Primary Examiner E. A. MILLER, Assistant Examiner US. Cl. X.R. 14922, 44, 61 

